1. Field of the Invention
The invention relates to an image reading apparatus for reading an object image and outputting an image signal.
2. Related Background Art
Hitherto, as shown in a cross sectional view of FIG. 11, an image sensor which is in contact with an original to be read and reads an image is constructed by: an image sensor board 2 on which a sensor IC 1 is installed; a lens array 3 for guiding a reflected light from the original illuminated by an illuminating unit 4 to the sensor IC 1; a cover glass 5 which is come into contact with the original; and a frame 6 for positioning and holding those component elements.
As an illuminating unit 4, a unit as shown in a cross sectional view and a top view of FIG. 12 is used. The illuminating unit 4 is constructed by: LEDs 7 of a lead frame type serving as light sources provided on both ends; an optical guide member 8 arranged in a longitudinal direction for converting a light irradiated from the LEDs into a line-shaped light; and a housing 9 having a square cross sectional shape for positioning and holding the LEDs 7 and optical guide member 8. An electric power is supplied to the LED 7 from a power source (not shown) through a lead 11.
When such an illuminating unit 4 is attached to the frame, as shown in FIG. 11, in order to illuminate the light from the oblique direction of 45° for the original, an attaching surface which is inclined by 45° for the original mounting surface is provided for the frame 6, and the surface corresponding to one side of a square in the cross section of the housing 9 constructing the illuminating unit 4 is come into contact with the inclined attaching surface and is adhered by both-side adhesive tape or the like, thereby positioning and fixing.
However, in the conventional image sensor mentioned above, since the housing of the illuminating unit having the square cross section is installed to the frame so as to be inclined by 45° for the original surface, there are the following problems.
(1) To enclose the illuminating unit into the frame, it is necessary that a length of diagonal line in the cross section of the housing of the illuminating unit is assured in the vertical direction in the frame. However, the image sensor main body cannot be largely formed. Therefore, a thickness of frame with which the lower portion of the illuminating unit is come into contact has to be made thin. It is difficult to work the frame. Even if the frame can be worked, a mechanical strength of the frame is insufficient.
(2) An angle at which the illuminating unit is attached to the frame is not equal to 45° depending on an individual difference of each image sensor and an optical axis is deviated, so that there is a case where an illuminance on the original reading line doesn't reach a specified value.
(3) To fix the illuminating unit to the frame, not only a material such as both-side adhesive tape or adhesive agent is necessary but also a step of attaching such a material is added, so that manufacturing costs rise.